Image sensor

ABSTRACT

An image sensor includes a pixel array including a plurality of unit pixels arranged along a plurality of rows and a plurality of columns. Each of the unit pixels includes a photoelectric conversion element generating and accumulating photocharges, a charge detection node receiving the photocharges accumulated in the photoelectric conversion element, a readout circuit converting the photocharges accumulated in and output from the charge detection node into an electrical pixel signal, the readout circuit outputting the electrical pixel signal, a capacitive element, and a switching element controlling connection between the charge detection node and the capacitive element. Each of the rows of the pixel array includes first pixels connected to a first conversion gain control line and second pixels connected to a second conversion gain control line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. application Ser.No. 16/838,517, filed Apr. 2, 2020, which is a Continuation Applicationof U.S. application Ser. No. 15/805,368, filed on Nov. 7, 2017, now U.S.Pat. No. 10,645,315 issued May 5, 2020, which claims priority fromKorean Patent Application No. 10-2016-0183465, filed on Dec. 30, 2016 inthe Korean Intellectual Property Office, the disclosures of which arehereby incorporated by reference in their entireties.

BACKGROUND

Example embodiments relate to an image sensor and, more particularly, toan image sensor having a wide dynamic range (WDR).

An image sensor converts an optical image into an electrical signal. Ascomputer and communication technologies have been developed,high-performance image sensors have been increasingly demanded invarious fields such as a digital camera, a camcorder, a personalcommunication system (PCS), a game console, a security camera, and amedical micro camera.

Image sensors may be categorized as charge coupled device (CCD) imagesensors or complementary metal-oxide-semiconductor (CMOS) image sensors.The CMOS image sensor may be simply driven. In addition, a signalprocessing circuit and an image sensing part of the CMOS image sensormay be integrated on a single chip. Thus, a size of the CMOS imagesensor may be reduced. Moreover, the CMOS image sensor may have a verylow power consumption so as to be easily applied to a product having alimited battery capacity. Furthermore, the CMOS image sensor may have ahigh resolution by the use of a CMOS technique. Accordingly, the CMOSimage sensor is widely used in various fields.

SUMMARY

Example embodiments may provide an image sensor having improved opticalcharacteristics.

According to an aspect of an example embodiment, there is provided animage sensor including a pixel array including a plurality of unitpixels arranged along a plurality of rows and a plurality of columns.Each of the plurality of unit pixels includes: a photoelectricconversion element configured to generate and accumulate photocharges; acharge detection node configured to receive the photocharges that areaccumulated in the photoelectric conversion element; a readout circuitconfigured to convert the photocharges that are received by the chargedetection node into an electrical signal, and to output the electricalsignal; a capacitive element; and a switching element configured tocontrol a connection between the charge detection node and thecapacitive element. Each of the plurality of rows of the pixel arrayincludes first pixels from among the plurality of unit pixels, andsecond pixels from among the plurality of unit pixels. The first pixelsare connected to a first conversion gain control line, and the secondpixels are connected to a second conversion gain control line.

According to an aspect of another example embodiment, there is providedan image sensor including a pixel array including a plurality of unitpixels arranged along a plurality of rows and a plurality of columns.Each of the plurality of unit pixels includes a photoelectric conversionelement configured to generate and accumulate photocharges; a chargedetection node configured to receive the photocharges that areaccumulated in the photoelectric conversion element; a readout circuitconfigured to convert the photocharges that are received by the chargedetection node into an electrical signal, and to output the electricalsignal; a capacitive element; and a switching element configured tocontrol a connection between the charge detection node and thecapacitive element. Each of the plurality of rows of the pixel arrayincludes first pixels from among the plurality of unit pixels, andsecond pixels from among the plurality of unit pixels. The first pixelshave a first conversion gain and the second pixels have a secondconversion gain.

According to an aspect of another example embodiment, there is providedan image sensor including a pixel array including first pixels andsecond pixels that are arranged in a plurality of rows and a pluralityof columns of a matrix. Each the first pixels and each of the secondpixels being configured to convert light that is incident thereon intoan electrical signal. Each of the plurality of rows includes at leastone of the first pixels and at least one of the second pixels. The firstpixels have a first conversion gain that is varied according to a firstamount of the light that is incident on the first pixels, and the secondpixels have a second conversion gain that is varied according to asecond amount of the light that is incident on the second pixels.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become apparent and more readilyappreciated from the following description of the example embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic block diagram illustrating an image processingdevice according to an example embodiment;

FIG. 2 is a schematic block diagram illustrating an image sensoraccording to an example embodiment;

FIG. 3 is a schematic diagram illustrating a pixel array of an imagesensor according to an example embodiment;

FIGS. 4A, 4B, 4C and 4D are circuit diagrams illustrating a unit pixelof a pixel array according to example embodiments;

FIG. 5 is a circuit diagram illustrating a pixel array of an imagesensor according to an example embodiment;

FIGS. 6A, 7A, 8A and 9A are timing diagrams illustrating operation ofthe pixel array according to the example embodiment of FIG. 5 ;

FIGS. 6B, 7B, 8B and 9B are views illustrating characteristic changes ofthe pixel array according to the timing diagrams of FIGS. 6A, 7A, 8A and9A, respectively;

FIGS. 10A and 10B are diagrams illustrating potential levels of a unitpixel in operation of an image sensor according to example embodiments;

FIGS. 11A and 12A are schematic diagrams illustrating pixel arrays ofimage sensors according to example embodiments.

FIGS. 11B and 12B are views illustrating characteristic changes of thepixel arrays in operation of the image sensors of FIGS. 11A and 12A,respectively;

FIG. 13A is a schematic diagram illustrating a pixel array of an imagesensor according to an example embodiment;

FIG. 13B is a view illustrating a characteristic change of the pixelarray in operation of the image sensor of FIG. 13A;

FIG. 14A is a schematic diagram illustrating a pixel array of an imagesensor according to an example embodiment;

FIG. 14B is a view illustrating a characteristic change of the pixelarray in operation of the image sensor of FIG. 14A;

FIG. 15 is a schematic diagram illustrating a pixel array of an imagesensor according to an example embodiment; and

FIG. 16 is a timing diagram illustrating operation of the image sensorof FIG. 15 .

DETAILED DESCRIPTION

Image sensors according to example embodiments will be describedhereinafter in detail with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram illustrating an image processingdevice according to an example embodiment.

Referring to FIG. 1 , an image processing device 100 may include animage sensor 110, an image signal processor 120, a display 130, and astorage 140.

The image processing device 100 may be an electronic device thatcaptures external images, such as a smart phone or a digital camera.

The image sensor 110 may convert an image of an external object intoelectrical signals or data signals. The image sensor 110 may include aplurality of pixels. Each of the plurality of pixels may receive lightreflected from the external object and may convert the received lightinto an electrical image signal or a photo signal.

The image signal processor 120 may process frame data FR (i.e., imagedata or photo data) received from the image sensor 110 and may outputcorrected image data IMG. For example, the image signal processor 120may perform one or more signal processing operations (e.g., colorinterpolation, color correction, gamma correction, color spaceconversion, and/or edge correction) on the received frame data FR togenerate the image data IMG.

The display 130 may display the image data IMG received from the imagesignal processor 120 such that a user may view the image data IMG. Forexample, the display 130 may include any of various display panels suchas a liquid crystal display panel, a light emitting diode (LED) displaypanel, an organic light emitting diode (OLED) display panel, anelectrophoretic display panel, and an electrowetting display panel. Thedisplay 130 may display the image data IMG through the display panel.

The storage 140 may store the image data IMG received from the imagesignal processor 120. The storage device 14 may include a volatilememory device (e.g., a static random access memory (SRAM) device, adynamic RAM (DRAM) device, and/or a synchronous DRAM (SDRAM) device)and/or a non-volatile memory device (e.g., a read only memory (ROM)device, a programmable ROM (PROM) device, an electrically programmableROM (EPROM) device, an electrically erasable and programmable ROM(EEPROM) device, a FLASH memory device, a phase-change RAM (PRAM)device, a magnetic RAM (MRAM) device, a resistive RAM (RRAM) device,and/or a ferroelectric RAM (FRAM) device).

FIG. 2 is a schematic block diagram illustrating an image sensor 110according to an example embodiment.

Referring to FIG. 2 , the image sensor 110 may include a pixel array 10,a row decoder 20, a row driver 30, a column decoder 40, a timinggenerator 50, a correlated double sampler (CDS) 60, an analog-to-digitalconverter (ADC) 70, and an input/output (I/O) buffer 80.

The pixel array 10 may include a plurality of unit pixels arranged in amatrix of rows and columns and may convert light incident on the unitpixels into electrical signals. The pixel array 10 may be driven by aplurality of driving signals (e.g., a selection signal, a reset signal,and/or a charge transfer signal) provided from the row decoder 20.

The row decoder 20 may provide the driving signals to the unit pixels ina unit of a row. The electrical signals converted in the pixel array 10may be provided to the correlated double sampler 60 in response to thedriving signals.

The row driver 30 may provide the driving signals for driving the unitpixels to the pixel array 10 in response to results decoded in the rowdecoder 20. In the event that the unit pixels are arranged in a matrixform, the driving signals may be provided in the unit of the row.

The timing generator 50 may supply control signals (e.g., clock signalsand a timing control signal) to control operations the row decoder 20and the column decoder 40, the correlated double sampler 60, theanalog-to-digital converter 70, and the I/O buffer 80. The timinggenerator 50 may include a logic control circuit, a phase lock loop(PLL) circuit, a timing control circuit, and/or a communicationinterface circuit.

The correlated double sampler 60 may receive the electrical signalsgenerated by the pixel array 10 and may hold and sample the receivedelectrical signals. The correlated double sampler 60 may doubly sample aspecific noise level and a signal level of the electrical signal and mayoutput a difference level corresponding to a difference between thenoise level and the signal level.

The analog-to-digital converter 70 may convert an analog signal, whichcorresponds to the difference level output from the correlated doublesampler 60, into a digital signal and output the digital signal.

The I/O buffer 80 may latch the digital signals output from theanalog-to-digital converter 70 and may sequentially output the latcheddigital signals to an image signal processor (e.g., the image signalprocessor 120 of FIG. 1 ) in response to results decoded in the columndecoder 40.

FIG. 3 is a schematic diagram illustrating a pixel array 10 of an imagesensor according to an example embodiment.

Referring to FIG. 3 , the pixel array 10 may include a plurality of unitpixels R, B, Gb, and Gr arranged along a plurality of rows Row1, Row2,Row3, and Row4 and a plurality of columns, a plurality of driving signallines RG_((i)) to RG_((i+3)), TG_((i)) to TG_((i+3)), SG_((i)) toSG_((i+3)), CG1 _((i)) to CG1 _((i+3)), and CG2 _((i)) to CG2 _((i+3)),and output lines VOUT. For example, FIG. 3 illustrates a 4×4 pixel array10. For example, the 4×4 pixel array 10 may be repeated along a rowdirection and a column direction.

An electrical signal may be generated by incident light in each of theunit pixels R, B, Gb, and Gr, and the unit pixels R, B, Gb, and Gr maybe driven by driving signals transmitted through charge transfer linesTG_((i)) to TG_((i+3)), reset lines RG_((i)) to RG_((i+3)), andselection lines SG_((i)) to SG_((i+3)).

The driving signal lines RG_((i)) to RG_((i+3)), TG_((i)) to TG_((i+3)),SG_((i)) to SG_((i+3)), CG1 _((i)) to CG1 _((i+3)), and CG2 _((i)) toCG2 _((i+3)) may extend in the row direction (e.g., a horizontaldirection) to drive the unit pixels R, B, Gb, and Gr included in thesame row at the same time. In some example embodiments, the drivingsignal lines may include the charge transfer lines TG_((i)) toTG_((i+3)), the reset lines RG_((i)) to RG_((i+3)), the selection linesSG_((i)) to SG_((i+3)), first conversion gain control lines CG1 _((i))to CG1 _((i+3)), and second conversion gain control lines CG2 _((i)) toCG2 _((i+3)). The charge transfer lines TG_((i)) to TG_((i+3)), thereset lines RG_((i)) to RG_((i+3)), and the selection lines SG_((i)) toSG_((i+3)) may be connected in common to the unit pixels R, B, Gb, andGr of a same row. The output lines V_(OUT) may extend in the columndirection (e.g., a vertical direction), and each of the output linesV_(OUT) may be connected in common to the unit pixels R, B, Gb, and Grarranged in a same column.

Each of the unit pixels R, B, Gb, and Gr may include a photoelectricconversion element and three, four, five, or six MOS transistorsconstituting a readout circuit. In some example embodiments, the unitpixels R, B, Gb, and Gr may have the same circuit elements, and thiswill be described later with reference to FIGS. 4A to 4D.

The photoelectric conversion elements of the unit pixels R, B, Gb, andGr may generate and accumulate photocharges in proportion to the amountof incident light. The photoelectric conversion elements of the unitpixels R, B, Gb, and Gr may have substantially the same full wellcapacity, and the amounts of photocharges generated and accumulated inthe photoelectric conversion elements may be different from each otherby environments (low illumination and high illumination) in which animage is taken. For example, the photoelectric conversion element mayinclude a photodiode, a photo transistor, a photo gate, a pinnedphotodiode (PPD), or any combination thereof.

Since low-illumination light and high-illumination light may be incidenton the pixel array 10 at the same time when an image is taken orobtained, the amounts of photocharges generated and accumulated in thephotoelectric conversion elements may be different according to theamounts of light incident on the unit pixels R, B, Gb, and Gr. In otherwords, the unit pixels R, B, Gb, and Gr on which the low-illuminationlight is incident may generate a small amount of photocharges, and thusit is required to improve sensitivity of the unit pixels R, B, Gb, andGr provided with the low-illumination light. On the contrary, the unitpixels R, B, Gb, and Gr on which the high-illumination light is incidentmay generate a large amount of photocharges, and thus it is required toreduce noise of the unit pixels R, B, Gb, and Gr provided with thehigh-illumination light. However, according to some example embodiments,gains of the unit pixels R, B, Gb, and Gr may be individually controlledor adjusted to enlarge or increase a dynamic range of the image sensor.Thus, a bright region (or a high-illumination region) and a dark region(or a low-illumination region) of an image may be clearly realized atthe same time.

In more detail, in each of the rows Row1, Row2, Row3, and Row4, of thepixel array 10, each of the unit pixels R, B, Gb, and Gr may beconnected to one of the first conversion gain control lines CG1 _((i)),CG1 _((i+1)), CG1 _((i+2)), and CG1 _((i+3)) or one of the secondconversion gain control lines CG2 _((i)), CG2 _((i+1)), CG2 _((i+2)),and CG2 _((i+3)), and conversion gains of the unit pixels R, B, Gb, andGr may be variable according to first conversion gain control signalsprovided through the first conversion gain control lines CG1(i),CG1(i+1), CG1(i+2), and CG1(i+3) and second conversion gain controlsignals provided through the second conversion gain control linesCG2(i), CG2(i+1), CG2(i+2), and CG2(i+3). The first conversion gaincontrol signal and the second conversion gain control signal may bevaried according to an illumination amount of light incident on thepixel array 10.

In more detail, each of the rows Row1, Row2, Row3, and Row4 of the pixelarray 10 may include first pixels connected to one of the firstconversion gain control lines CG1 _((i)), CG1 _((i+1)), CG1 _((i+2)),and CG1 _((i+3)) and second pixels connected to one of the secondconversion gain control lines CG2 _((i)), CG2 _((i+1)), CG2 _((i+2)),and CG2 _((i+3)). Each of the first and second pixels may have a firstconversion gain or a second conversion gain by each of the first orsecond conversion gain control signals provided through the firstconversion gain control lines CG1(i), CG1(i+1), CG1(i+2), and CG1(i+3)and the second conversion gain control signals provided through thesecond conversion gain control lines CG2(i), CG2(i+1), CG2(i+2), andCG2(i+3).

In some example embodiments, the first pixels and the second pixels maybe arranged in a form of a checkerboard mosaic pattern. Thus, the firstpixels may be arranged in a stepped pattern in a diagonal direction, andthe second pixels may be arranged in a pattern shape in the diagonaldirection. In more detail, the number (i.e., a first number) of thefirst pixels may be different from the number (i.e., a second number) ofthe second pixels in each of the rows Row1, Row2, Row3, and Row4. Inaddition, the number (i.e., a first number) of the first pixels disposedin odd-numbered rows Row1 and Row3 may be different from the number(i.e., a second number) of the first pixels disposed in even-numberedrows Row2 and Row4. Likewise, the number (i.e., a first number) of thefirst pixels may be different from the number (i.e., a second number) ofthe second pixels in each of the columns. In addition, the number (i.e.,a first number) of the first pixels disposed in an odd-numbered columnmay be different from the number (i.e., a second number) of the firstpixels disposed in an even-numbered column.

For example, in the 4×4 pixel array 10, one first pixel and three secondpixels may be disposed in each of the odd-numbered rows Row1 and Row3,and three first pixels and one second pixel may be disposed in each ofthe even-numbered rows Row2 and Row4. Three first pixels and one secondpixel may be disposed in each of the odd-numbered columns, and one firstpixel and three second pixels may be disposed in each of theeven-numbered columns. In other words, in each of the odd-numbered rowsRow1 and Row3, one of the first conversion gain control lines CG1 _((i))and CG1 _((i+2)) may be connected to one of the unit pixels R, B, Gb,and Gr and one of the second conversion gain control lines CG2 _((i))and CG2 _((i+2)) may be connected to a remaining three of the unitpixels R, B, Gb, and Gr. In each of the even-numbered rows Row2 andRow4, one of the first conversion gain control lines CG1 _((i+1)) andCG1 _((i+3)) may be connected to three of the unit pixels R, B, Gb, andGr and one of the second conversion gain control lines CG2 _((i+1)) andCG2 _((i+3)) may be connected to a remaining one of the unit pixels R,B, Gb, and Gr.

In addition, each of the unit pixels R, B, Gb, and Gr may include acolor filter having three colors or four colors. In other words, each ofthe first and second pixels according to some example embodiments mayinclude a blue color filter (B), a red color filter (R), or a greencolor filter (Gb or Gr). However, embodiments are not limited thereto.In some example embodiments, the unit pixels R, B, Gb, and Gr of thepixel array 10 may include color filters that transmit magenta (Mg)light, yellow (Y) light, cyan (Cy) light, and/or white (W) light. One orsome of the unit pixels R, B, Gb, and Gr may include an infrared filter(Z) that transmits infrared light.

In detail, first color filters (red color filters (R) or blue colorfilters (B)) and second color filters (green color filters (Gb and Gb))may be alternately arranged in each of the rows Row1, Row2, Row3, andRow4. Each of the color filters may receive light having a correspondingcolor. For example, the blue color filters (B) and the green colorfilters (Gb) may be alternately arranged in each of the odd-numberedrows Row1 and Row3, and the red color filters (R) and the green colorfilters (Gr) may be alternately arranged in each of the even-numberedrows Row2 and Row4. Here, the blue color filters (B) and the red colorfilters (R) may be arranged in a diagonal direction. In other words, thegreen color filters (Gb or Gr) relative to a brightness signal may bedisposed in all of the rows Row1, Row2, Row3, and Row4, the blue colorfilters (B) may be disposed in the odd-numbered rows Row1 and Row3, andthe red color filters (R) may be disposed in the even-numbered rows Row2and Row4. Thus, a resolution of the image sensor may be improved.

FIGS. 4A, 4B, 4C 4D are circuit diagrams illustrating a unit pixel of apixel array according to example embodiments.

Referring to FIGS. 4A, 4B, 4C and 4D, a unit pixel may include aphotoelectric conversion element PD, a transfer transistor TX, a readoutcircuit, and a conversion gain variable circuit. Here, the readoutcircuit may include a reset transistor RX, a selection transistor SX,and a drive transistor DX. The conversion gain variable circuit mayinclude a conversion gain transistor CGX and a capacitor CAP.

In more detail, the photoelectric conversion element PD may generate andaccumulate photocharges corresponding to incident light. For example,the photoelectric conversion element PD may include a photodiode, aphoto transistor, a photo gate, a pinned photodiode (PPD), or anycombination thereof.

The transfer transistor TX may transfer the photocharges accumulated inthe photoelectric conversion element PD to a charge detection node FD(i.e., a floating diffusion region). The charge transfer line TG may beconnected a transfer gate electrode of the transfer transistor TX, andthe transfer transistor TX may be controlled by the charge transfersignal provided by the charge transfer line TG to the transfer gateelectrode.

The charge detection node FD may receive the photocharges generated inthe photoelectric conversion element PD and may cumulatively store thereceived photocharges. The drive transistor DX may be controlledaccording to the amount of the photocharges accumulated in the chargedetection node FD.

The reset transistor RX may periodically reset photocharges accumulatedin the charge detection node FD. In detail, a drain terminal of thereset transistor RX may be connected to the charge detection node FD,and a source terminal of the reset transistor RX may be connected to apixel power voltage V_(PIX). When the reset transistor RX is turned on,the pixel power voltage V_(PIX) connected to the source terminal of thereset transistor RX may be transmitted to the charge detection node FD.Thus, the photocharges accumulated in the charge detection node FD maybe discharged to reset the charge detection node FD when the resettransistor RX is turned on.

A gate electrode of the drive transistor DX may be connected to thecharge detection node FD. The drive transistor DX may be a sourcefollower buffer amplifier that generates a source-drain current inproportion to the amount of the photocharges of the charge detectionnode FD. The drive transistor DX may amplify a variation in potential ofthe charge detection node FD and may output the amplified signal to theoutput line V_(OUT) through the selection transistor SX. A sourceterminal of the drive transistor DX may be connected to the pixel powervoltage V_(PIX), and a drain terminal of the drive transistor DX may beconnected to a source terminal of the selection transistor SX.

The photocharges stored in the charge detection node FD may be convertedinto an electrical signal, which is represented by the followingEquation 1, through the drive transistor DX.V=q/C _(FD)  [Equation 1]

In Equation 1, “V” is an output voltage, “q” is the amount ofphotocharges generated by light, and “C_(FD)” is a capacitance of thecharge detection node FD.

In other words, a conversion gain of the drive transistor DX outputtingthe electrical signal in proportion to the amount of the photochargesdetected in the charge detection node FD may be varied according to thecapacitance of the charge detection node FD.

The selection transistor SX may select the unit pixels to be sensed inthe unit of row. The selection line SG may be connected to a selectiongate electrode of the selection transistor SX. When the selectiontransistor SX is turned on by the selection signal provided by theselection line G, the electrical signal output from the drain terminalof the drive transistor DX may be output to the output line V_(OUT).

The conversion gain variable circuit may vary the capacitance of thecharge detection node FD to vary the conversion gain of the unit pixel.In some example embodiments, the unit pixel may have a first conversiongain or a second conversion gain.

The conversion gain transistor CGX may be connected in series betweenthe charge detection node FD and a first terminal of the capacitor CAP.A gate electrode of the conversion gain transistor CGX may be connectedto the first conversion gain control line CG1 or the second conversiongain control line CG2, and the conversion gain transistor CGX mayconnect the capacitor CAP to the charge detection node FD by the firstconversion gain control signal provided by the first conversion gaincontrol line CG1 or the second conversion gain control signal providedby the second conversion gain control line CG2.

According to the example embodiment illustrated in FIG. 4A, the firstterminal of the capacitor CAP may be connected to the conversion gaintransistor CGX, and a second terminal of the capacitor CAP may beconnected to a ground. The capacitor CAP may be connected to the chargedetection node FD when the conversion gain transistor CGX is turned on,and thus the capacitance of the charge detection node FD may beincreased. In other words, since an input impedance of the drivetransistor DX increases, the unit pixel may have a low conversion gain.On the contrary, when the conversion gain transistor CGX is turned off,the capacitor CAP may be electrically isolated from the charge detectionnode FD. In this case, the unit pixel may have a high conversion gain.

According to the example embodiment illustrated in FIG. 4B, thecapacitor CAP may be connected between the conversion gain transistorCGX and the pixel power voltage V_(PIX).

According to the example embodiment illustrated in FIG. 4C, a unit pixelmay include a first photoelectric conversion element PD1, a secondphotoelectric conversion element PD2, a first transfer transistor TX1and a second transfer transistor TX2. The first transfer transistor TX1and the second transfer transistor TX2 may share the charge detectionnode FD (i.e., a floating diffusion region).

A transfer gate electrode of the first transfer transistor TX1 may beconnected to a first charge transfer line TG1, and the first transfertransistor TX1 may transfer photocharges accumulated in the firstphotoelectric conversion element PD1 to the charge detection node FD(i.e., floating diffusion region) by a first charge transfer signalprovided by the first charge transfer line TG1.

A transfer gate electrode of the second transfer transistor TX2 may beconnected to a second charge transfer line TG2, and the second transfertransistor TX2 may transfer photocharges accumulated in the secondphotoelectric conversion element PD2 to the charge detection node FD(i.e., floating diffusion region) by a second charge transfer signalprovided by the second charge transfer line TG2.

According to the example embodiment illustrated in FIG. 4D, a unit pixelmay include first photoelectric conversion element PD1, a secondphotoelectric conversion element PD2, a third photoelectric conversionelement PD3, a fourth photoelectric conversion element PD4, a firsttransfer transistor TX1, a second transfer transistor TX2, a thirdtransfer transistor TX3, and a fourth transfer transistor TX4. The firsttransfer transistor TX1, the second transfer transistor TX2, the thirdtransfer transistor TX3, and the fourth transfer transistor TX4 mayshare the charge detection node FD. The first transfer transistor TX1,the second transfer transistor TX2, the third transfer transistor TX3,and the fourth transfer transistor TX4 may be connected to a firstcharge transfer lines TG1, a second charge transfer line TG2, a thirdcharge transfer line TG3, and a fourth charge transfer line TG4,respectively.

A transfer gate electrode of the first transfer transistor TX1 may beconnected to the first charge transfer line TG1, and the first transfertransistor TX1 may transfer photocharges accumulated in the firstphotoelectric conversion element PD1 to the charge detection node FD(i.e., floating diffusion region) by a first charge transfer signalprovided by the first charge transfer line TG1.

A transfer gate electrode of the second transfer transistor TX2 may beconnected to the second charge transfer line TG2, and the secondtransfer transistor TX2 may transfer photocharges accumulated in thesecond photoelectric conversion element PD2 to the charge detection nodeFD by a second charge transfer signal provided by the second chargetransfer line TG2.

A transfer gate electrode of the third transfer transistor TX3 may beconnected to the third charge transfer line TG3, and the third transfertransistor TX3 may transfer photocharges accumulated in the thirdphotoelectric conversion element PD3 to the charge detection node FD bya third charge transfer signal provided by the third charge transferline TG3.

A transfer gate electrode of the fourth transfer transistor TX4 may beconnected to the fourth charge transfer line TG4, and the fourthtransfer transistor TX4 may transfer photocharges accumulated in thefourth photoelectric conversion element PD4 to the charge detection nodeFD by a fourth charge transfer signal provided by the fourth chargetransfer line TG4.

Accordingly, as illustrated in FIGS. 4C and 4D, a unit pixel may includea plurality of photoelectric conversion elements and a plurality oftransfer transistors.

FIG. 5 is a circuit diagram illustrating a pixel array of an imagesensor according to an example embodiment.

Referring to FIG. 5 , unit pixels R, B, Gb, and Gr may be arranged alongrows Row1, Row2, Row3, and Row4 and columns, and each of the rows Row1,Row2, Row3, and Row4 may include both first and second pixels. In someexample embodiments, each of the first and second pixels may include thephotoelectric conversion element PD, the transfer transistor TX, thereset transistor RX, the drive transistor DX, the selection transistorSX, the conversion gain transistor CGX, and the capacitor CAP, which aredescribed with reference to FIG. 4A. Alternatively, each of the firstand second pixels may include the elements of FIG. 4B, 4C, or 4D.

A 4×4 pixel array 10 is illustrated as an example in FIG. 5 . Forexample, as described with reference to FIG. 3 , each of odd-numberedrows Row1 and Row3 may include one first pixel and three second pixels,and each of the even-numbered rows Row2 and Row4 may include three firstpixels and one second pixel.

In each of the rows Row1, Row2, Row3, and Row4, the conversion gaintransistors CGX of the first pixels may be connected to one of the firstconversion gain control lines CG1 _((i)), CG1 _((i+1)), CG1 _((i+2)),and CG1 _((i+3)) and the conversion gain transistors CGX of the secondpixels may be connected to one of the second conversion gain controllines CG2 _((i)), CG2 _((i+1)), CG2 _((i+2)), and CG2 _((i+3)).

In some example embodiments, the first conversion gain control signalmay be provided from the row driver 30 of FIG. 2 to the first conversiongain control lines CG1 _((i)), CG1 _((i+1)), CG1 _((i+2)), and CG1_((i+3)) based on a first illumination amount of light incident on thefirst pixels, and the second conversion gain control signal may beprovided from the row driver 30 of FIG. 2 to the second conversion gaincontrol lines CG2 _((i)), CG2 _((i+1)), CG2 _((i+2)), and CG2 _((i+3))based on a second illumination amount of light incident on the secondpixels. The conversion gains of the first and second pixels may bevaried according to the first and second conversion gain controlsignals. These will be described in more detail with reference to FIGS.6A to 9B.

FIGS. 6A, 7A, 8A and 9A are timing diagrams illustrating operation ofthe pixel array according to the example embodiment of FIG. 5 . FIGS.6B, 7B, 8B and 9B are views illustrating characteristic changes of thepixel array according to the timing diagrams of FIGS. 6A, 7A, 8A and 9A,respectively. FIGS. 6B, 7B, 8B and 9B illustrate an 8×8 pixel array 10as an example. In addition, FIGS. 6B, 7B, 8B and 9B illustratearrangement of high-illumination pixels LCG having a first conversiongain and low-illumination pixels HCG having a second conversion gain.Furthermore, the reference designators R, Gr, B, and Gb show arrangementof color filters in FIGS. 6B, 7B, 8B and 9B.

Referring to FIGS. 5, 6A, and 6B, operation of the unit pixels mayinclude a reset mode of resetting the photoelectric conversion elementsPD and the charge detection nodes FD, a light integration mode EIT ofintegrating or accumulating photocharges in the photoelectric conversionelements PD, and a read out mode of outputting electrical signalscorresponding to the accumulated photocharges. Here, the lightintegration mode EIT may mean an effective integration time of light.

In the reset mode, the reset signal RG and the charge transfer signal TGmay be activated to turn on the reset transistor RX and the transfertransistor TX. Thus, the pixel power voltage V_(PIX) may be provided tothe charge detection node FD. As a result, photocharges in thephotoelectric conversion element PD and the charge detection node FD maybe discharged to reset the photoelectric conversion element PD and thecharge detection node FD.

The light integration mode EIT may be performed after resetting thephotoelectric conversion element PD and the charge detection node FD.Photocharges may be generated and accumulated in the photoelectricconversion element PD until the transfer transistor TX is turned onagain after the transfer transistor TX is turned off after completion ofthe reset mode (i.e., for a photoelectric conversion time). In someexample embodiments, all of the unit pixels of the pixel array 10 may beexposed to light for the same time. In other words, all of the unitpixels may integrate photocharges for the same photoelectric conversiontime. At this time, since light is reflected from an object having botha low-illumination region and a high-illumination region and then isincident on the pixel array 10, the amount of photocharges generated inone or more unit pixels may be different from the amount of thephotocharges generated in one or more other unit pixels. Thus, the firstand second conversion gain control signals may be controlled to vary theconversion gains of the unit pixels.

For example, after the start of the integration of the photocharges andbefore reactivation of the charge transfer signal TG, the firstconversion gain control signal CG1 may be activated and the secondconversion gain control signal CG2 may be inactivated. Thus, in a rowselected by the selection signal SG, the conversion gain transistors CGXof the first pixels may be turned on to increase the capacitances of thecharge detection nodes FD of the first pixels, and the conversion gaintransistors CGX of the second pixels may be turned off to maintain thecapacitances of the charge detection nodes FD of the second pixels. Inother words, the capacitances of the charge detection nodes FD of thesecond pixels may not be varied. As a result, the first pixels may havea first conversion gain (e.g., a low conversion gain), and the secondpixels may have a second conversion gain (e.g., a high conversion gain)that is higher than the first conversion gain. In other words, the firstpixels may be high-illumination pixels LCG that have a low conversiongain and convert optical signals obtained from a bright portion (i.e.,the high-illumination region) of the object into electrical signals. Thehigh-illumination pixels LCG may output the converted electrical signalsas first pixel signals. The second pixels may be low-illumination pixelsHCG that have a high conversion gain and convert optical signalsobtained from a dark portion (i.e., the low-illumination region) of theobject into electrical signals. The low-illumination pixels HCG mayoutput the converted electrical signals as second pixel signals. Thus, ahigh-illumination image may be obtained from the first pixels, and alow-illumination image may be obtained from the second pixels.

After controlling the conversion gains of the first and second pixels,the reset signal RG may be inactivated. At this time, a reset potentialof the charge detection nodes FD of the first and second pixels may bedetected to output a reference signal.

After outputting the reference signal, the charge transfer signal TG maybe activated to transfer the photocharges integrated or accumulated inthe photoelectric conversion element PD into the charge detection nodeFD. Potentials of the charge detection nodes FD may be detected afterthe charge transfer signal TG is inactivated, and thus the first andsecond pixel signals may be output from the first and second pixels,respectively. In other words, the high-illumination and low-illuminationpixel signals in each of the rows may be output at the same time. As aresult, a dynamic range of an image in which the low-illumination regionand the high-illumination region are mixed with each other may beenlarged or increased in real time.

According to the example embodiment illustrated in FIGS. 7A and 7B, thefirst and second conversion gain control signals CG1 and CG2 may beinput to the unit pixels of each of the rows opposite to that of theexample embodiment of FIG. 6A. In this case, the first pixels may havethe second conversion gain (e.g., the high conversion gain), and thesecond pixels may have the first conversion gain (e.g., the lowconversion gain).

Thus, as illustrated in FIG. 7B, the high-illumination pixels LCG andthe low-illumination pixels HCG may be arranged opposite to thearrangement of FIG. 6B, and the first and second pixel signals may beoutput opposite to that of the example embodiment of FIG. 6B. As aresult, the low-illumination image may be obtained from the firstpixels, and the high-illumination image may be obtained from the secondpixels.

According to the example embodiment illustrated in FIGS. 8A and 8B, allof the first and second conversion gain control signals CG1 and CG2 maybe activated to be input to the pixel array 10. In this case, since thecapacitances of the charge detection nodes FD of the first and secondpixels are increased, the first and second pixels may have the firstconversion gain (e.g., the low conversion gain). Thus, as illustrated inFIG. 8B, all of the first and second pixels may be the high-illuminationpixels LCG which can obtain the high-illumination image of which noiseis reduced.

According to the example embodiment illustrated in FIGS. 9A and 9B, allof the first and second conversion gain control signals CG1 and CG2 maybe inactivated to be input to the pixel array 10. In this case, sincethe capacitances of the charge detection nodes FD of the first andsecond pixels are not varied, the first and second pixels may have thesecond conversion gain (e.g., the high conversion gain). Thus, asillustrated in FIG. 9B, all of the first and second pixels may be thelow-illumination pixels HCG which can obtain the low-illumination imagewith improved sensitivity.

FIGS. 10A and 10B are diagrams illustrating potential levels of the unitpixels in operation of the pixel array of FIG. 5 . FIG. 10A illustratesa potential level of the low-illumination pixel HCG, and FIG. 10Billustrates a potential level of the high-illumination pixel LCG.

Referring to FIGS. 5 and 10A, since a small amount of light is incidenton the photoelectric conversion element PD of the low-illuminationpixel, a small amount of photocharges may fill the photoelectricconversion element PD of the low-illumination pixel.

In the low-illumination pixel, the charge detection node FD may have alow capacitance since the conversion gain transistor CGX is turned off.When the transfer transistor TX is turned on, the photochargesaccumulated in the photoelectric conversion element PD may betransferred into the charge detection node FD having the low capacitancein the low-illumination pixel.

Referring to FIGS. 5 and 10B, the photoelectric conversion element PD ofthe high-illumination pixel may be completely filled with photochargesby strong light incident on the photoelectric conversion element PD. Inthe high-illumination pixel, the conversion gain transistor CGX may beturned on to connect the capacitor CAP to the charge detection node FD,and thus the capacitance of the charge detection node FD may beincreased. At this time, the capacitance of the charge detection node FDmay be greater than a full well capacity of the photoelectric conversionelement PD. Thus, when the transfer transistor TX is turned on, thephotocharges accumulated in the photoelectric conversion element PD maybe transferred to the charge detection node FD having the increasedcapacitance.

FIGS. 11A and 12A are schematic diagrams illustrating pixel arrays ofimage sensors according to example embodiments. FIGS. 11B and 12B areviews illustrating characteristic changes of the pixel arrays inoperation of the image sensors of FIGS. 11A and 12A, respectively.Hereinafter, the same elements as described in the above exampleembodiments will be indicated by the same reference numerals or the samereference designators, and the descriptions thereto will be omitted ormentioned briefly for the purpose of ease and convenience inexplanation.

Referring to FIG. 11A, each of rows Row1, Row2, Row3, and Row4 of apixel array 10 may include both first and second pixels, and the firstpixels and the second pixels may be alternately arranged in a rowdirection and a column direction. In other words, the first pixels intwo adjacent rows may be arranged in a zigzag form in the row direction,and the second pixels in the two adjacent rows may also be arranged in azigzag form in the row direction. Likewise, the first pixels in twoadjacent columns may be arranged in a zigzag form in the columndirection, and the second pixels in the two adjacent columns may also bearranged in a zigzag form in the column direction. Each of the first andsecond pixels may have the circuit elements of FIG. 4A, 4B, 4C, or 4D.

As described above, in each of the rows Row1, Row2, Row3, and Row4, thefirst pixels may be connected to the first conversion gain control lineCG1 _((i)), CG1 _((i+1)), CG1 _((i+2)), or CG1 _((i+3)) and the secondpixels may be connected to the second conversion gain control line CG2_((i)), CG2 _((i+1)), CG2 _((i+2)), or CG2 _((i+3)). The first andsecond pixels may be controlled by the first and second conversion gaincontrol signals, respectively, based on an image environment.

In the example embodiment illustrated in FIG. 11A, when the firstconversion gain control signal is activated and the second conversiongain control signal is inactivated, the first pixels may be thehigh-illumination pixels LCG having the low conversion gain and thesecond pixels may be the low-illumination pixels HCG having the highconversion gain, as illustrated in FIG. 11B. In the example embodimentillustrated in FIG. 11A, when the first and second conversion gaincontrol signals are controlled differently, the low-illumination pixelsHCG and the high-illumination pixels LCG may be arranged opposite to thearrangement illustrated in FIG. 11B or all of the unit pixels may be thehigh-illumination pixels LCG or the low-illumination pixels HCG.

Referring to FIG. 12A, each of rows Row1, Row2, Row3, and Row4 of apixel array 10 may both include first and second pixels, and the firstpixels and the second pixels may be alternately arranged in a rowdirection. In addition, all of unit pixels in each of columns may be thefirst pixels or the second pixels.

In the example embodiment illustrated in FIG. 12A, when the firstconversion gain control signal is activated and the second conversiongain control signal is inactivated, the high-illumination pixels LCG andthe low-illumination pixels HCG may be alternately arranged asillustrated in FIG. 12B. Alternatively, when the first and secondconversion gain control signals are controlled differently, thelow-illumination pixels HCG and the high-illumination pixels LCG may bearranged opposite to the arrangement illustrated in FIG. 12B or all ofthe unit pixels may be the high-illumination pixels LCG or thelow-illumination pixels HCG.

FIG. 13A is a schematic diagram illustrating a pixel array of an imagesensor according to an example embodiment. FIG. 13B is a viewillustrating a characteristic change of the pixel array in operation ofthe image sensor of FIG. 13A. Hereinafter, the same elements asdescribed in the above example embodiments will be indicated by the samereference numerals or the same reference designators, and thedescriptions thereto will be omitted or mentioned briefly for thepurpose of ease and convenience in explanation.

Referring to FIGS. 13A and 13B, each of unit pixels B, R, and G mayinclude 2×2 sub-pixels sP and may have one color filter. In other words,the sub-pixels sP of each of the unit pixels B, R, and G may share thecolor filter having one color. For example, each of the unit pixels B,R, and G may include four photoelectric conversion elements PD and fourtransfer transistors which share one charge detection node FD, asillustrated in FIG. 4D. Each of the unit pixels B, R, and G includesfour sub-pixels sP in FIGS. 13A and 13B. However, example embodimentsare not limited thereto. In other example embodiments, each of the unitpixels B, R, and G may include two sub-pixels sP.

In some example embodiments, each of rows Row1, Row2, Row3, and Row4 ofa pixel array 10 may include first pixels connected to a firstconversion gain control line CG1 _((i)), CG1 _((i+1)), CG1 _((i+2)), orCG1 _((i+3)) and second pixels connected to a second conversion gaincontrol line CG2 _((i)), CG2 _((i+1)), CG2 _((i+2)), or CG2 _((i+3)).Conversion gains of the first pixels and the second pixels may be variedaccording to first conversion gain control signal and second conversiongain control signals, respectively. In each of the first pixels, thesub-pixels sP may be low-illumination pixels HCG or high-illuminationpixels LCG. Likewise, in each of the second pixels, the sub-pixels sPmay be low-illumination pixels HCG or high-illumination pixels LCG.

FIG. 14A is a schematic diagram illustrating a pixel array of an imagesensor according to an example embodiment. FIG. 14B is a viewillustrating a characteristic change of the pixel array in operation ofthe image sensor of FIG. 14A. Hereinafter, the same elements asdescribed in the above example embodiments will be indicated by the samereference numerals or the same reference designators, and thedescriptions thereto will be omitted or mentioned briefly for thepurpose of ease and convenience in explanation.

FIGS. 14A and 14B illustrate a 4×4 pixel array 10 as an example. Inaddition, FIGS. 14A and 14B illustrate arrangement of high-illuminationpixels LCG having a first conversion gain and low-illumination pixelsHCG having a second conversion gain and arrangement of color filters R,G, and B.

In some example embodiments, each of rows Row1, Row2, Row3, and Row4 ofa pixel array 10 may include first pixels connected to a firstconversion gain control line CG1 _((i)), CG1 _((i+1)), CG1 _((i+2)), orCG1 _((i+3)) and second pixels connected to a second conversion gaincontrol line CG2 _((i)), CG2 _((i+1)), CG2 _((i+2)), or CG2 _((i+3)).

Referring to FIGS. 14A and 14B, each of the first and second pixels mayinclude four sub-pixels sP sharing a color filter having the same color.The first pixels may be arranged in a stepped shape in a diagonaldirection, and the second pixels may be arranged in a stepped shape inthe diagonal direction. In more detail, as described with reference toFIG. 3 , the number of the first pixels may be different from the numberof the second pixels in each of the rows Row1, Row2, Row3, and Row4. Inaddition, the number of the first pixels disposed in odd-numbered rowsRow1 and Row3 may be different from the number of the first pixelsdisposed in even-numbered rows Row2 and Row4. Likewise, the number ofthe first pixels may be different from the number of the second pixelsin each of the columns. In addition, the number of the first pixelsdisposed in an odd-numbered column may be different from the number ofthe first pixels disposed in an even-numbered column.

FIG. 15 is a schematic diagram illustrating a pixel array of an imagesensor according to an example embodiment. FIG. 16 is a timing diagramillustrating operation of the image sensor of FIG. 15 . Hereinafter, thesame elements as described in the above example embodiments will beindicated by the same reference numerals or the same referencedesignators, and the descriptions thereto will be omitted or mentionedbriefly for the purpose of ease and convenience in explanation.

Referring to FIG. 15 , each of unit pixels R, B, Gb, and Gr may beconnected to a first or second conversion gain control line CG1 _((i)),CG1 _((i+1)), CG1 _((i+2)), or CG1 _((i+3)), CG2 _((i)), CG2 _((i+1)),CG2 _((i+2)), or CG2 _((i+3)) in each of rows Row1, Row2, Row3, and Row4of a pixel array 10. In addition, according to this example embodiment,each of unit pixels R, B, Gb, and Gr may be connected to a first orsecond charge transfer line TG1 _((i)), TG1 _((i+1)), TG1 _((i+2)), orTG1 _((i+3)), TG2 _((i)), TG2 _((i+1)), TG2 _((i+2)), or TG2 _((i+3)) ineach of the rows Row1, Row2, Row3, and Row4 of a pixel array 10.

Each of the unit pixels R, B, Gb, and Gr may include at least onephotoelectric conversion element PD, a readout circuit, and a conversiongain variable circuit. For example, each of the unit pixels R, B, Gb,and Gr may have the circuit elements of FIG. 4A, 4B, 4C, or 4D, asdescribed above.

According to this example embodiment, a conversion gain of each of theunit pixels R, B, Gb, and Gr may be varied by the first or secondconversion gain control signal, and a light integration time (i.e., alight exposure time) of each of the unit pixels R, B, Gb, and Gr may bevaried by a first or second charge transfer signal. For example, theconversion gain and the light integration time (i.e., first lightexposure time) of first pixels may be controlled independently of theconversion gain and the light integration time (i.e., second lightexposure time) of second pixels.

In some example embodiments, each of the rows Row1, Row2, Row3, and Row4may include the first pixels connected to the first conversion gaincontrol line CG1 _((i)), CG1 _((i+1)), CG1 _((i+2)), or CG1 _((i+3)) andthe second pixels connected to the second conversion gain control lineCG2 _((i)), CG2 _((i+1)), CG2 _((i+2)), or CG2 _((i+3)). In addition,the first pixels may be connected to the first charge transfer lines TG1_((i)) to TG1 _((i+3)), and the second pixels may be connected to thesecond charge transfer lines TG2 _((i)) to TG2 _((i+3)).

In some example embodiments, the first pixels may be controlled to havea first conversion gain and a first light integration time, and thesecond pixels may be controlled to have a second conversion gain and asecond light integration time.

For example, as illustrated in FIG. 16 , a first charge transfer signalTG1 may be provided to the first pixel. The first charge transfer signalmay be turned on again after a long time LIT after the photoelectricconversion element PD is reset. In addition, since the first conversiongain control signal CG1 which is inactivated is applied to the firstpixel, the conversion gain transistor CGX of the first pixel may beturned off. Thus, the first pixel may have a high conversion gain tooutput a pixel signal with improved sensitivity.

When high-illumination light is incident on the second pixel, a secondcharge transfer signal TG2 may be provided to the second pixel. Thesecond charge transfer signal TG2 may be turned on again after a shorttime SIT after the photoelectric conversion element PD is reset. Inaddition, since the second conversion gain control signal CG2 which isactivated is applied to the second pixel, the conversion gain transistorCGX of the second pixel may be turned on. Thus, the second pixel mayhave a low conversion gain to reduce noise of a pixel signal output fromthe second pixel.

In other words, when low-illumination light is incident on the firstpixels, the first pixels may have the high conversion gain and may beexposed to light for a long time. In addition, when high-illuminationlight is incident on the second pixels, the second pixels may have thelow conversion gain and may be exposed to light for a short time.

According to this example embodiment, the first and second pixels mayhave the conversion gains different from each other and exposure timesdifferent from each other, and thus a dynamic range of the image sensormay be enlarged or increased.

According to some example embodiments, the first pixels and the secondpixels may be disposed in each of the rows of the pixel array, and theconversion gain of the first pixels may be different from the conversiongain of the second pixels. Thus, the image sensor may detect thelow-illumination image and the high-illumination image at the same time.The conversion gain may be reduced in the pixels converting lightprovided from the high-illumination region, thereby reducing asignal-to-noise ratio. In addition, the conversion gain may be increasedin the pixels converting light provided from the low-illuminationregion, thereby improving the sensitivity. In other words, the dynamicrange may be enlarged or increased in the image in which thelow-illumination region and the high-illumination region are mixed witheach other. As a result, a clear image may be realized.

While example embodiments have been described, it will be apparent tothose skilled in the art that various changes and modifications may bemade without departing from the spirit and scope of the inventiveconcept. Therefore, it should be understood that the above exampleembodiments are not limiting, but illustrative. Thus, the scope of theinventive concept is to be determined by the broadest permissibleinterpretation of the following claims and their equivalents, and shallnot be restricted or limited by the foregoing description.

What is claimed is:
 1. An image sensor comprising: a first pixel groupsharing a first color filter, the first pixel group being configured toshare a first conversion gain transistor, a first reset transistor, afirst floating diffusion region, a first driving transistor, and a firstselection transistor; and a second pixel group sharing a second colorfilter, the second pixel group being disposed directly adjacent to thefirst pixel group in a first direction and is configured to share asecond conversion gain transistor, a second reset transistor, a secondfloating diffusion region, a second driving transistor, and a secondselection transistor, wherein the first conversion gain transistor isconnected to the first floating diffusion region and is connected to thefirst reset transistor in series, wherein the second conversion gaintransistor is connected to the second floating diffusion region and isconnected to the second reset transistor in series, and wherein each ofthe first pixel group and the second pixel group comprises 2×2photoelectric conversion elements.
 2. The image sensor of claim 1,wherein the first color filter is a green color filter and the secondcolor filter is a red color filter.
 3. The image sensor of claim 2,further comprising: a third pixel group sharing a third color filter,the third pixel group being disposed directly adjacent to the firstpixel group in a second direction perpendicular to the first direction;and a fourth pixel group sharing a fourth color filter, the fourth pixelgroup being disposed directly adjacent to the third pixel group in thefirst direction, wherein the first pixel group and the third pixel groupare connected to a first output line, wherein the second pixel group andthe fourth pixel group are connected to a second output line differentfrom the first output line, wherein each of the third pixel group andthe fourth pixel group comprises 2×2 photoelectric conversion elements,and wherein the first output line and the second output line extend inthe second direction.
 4. The image sensor of claim 1, wherein the firstcolor filter is a blue color filter and the second color filter is agreen color filter.
 5. The image sensor of claim 4, wherein the firstconversion gain transistor and the second conversion gain transistor areconnected to a conversion gain control line.
 6. The image sensor ofclaim 5, wherein the first floating diffusion region has a first fullwell capacity when the first conversion gain transistor is turned offand the first floating diffusion region has a second full well capacitygreater than the first full well capacity when the first conversion gaintransistor is turned on in response to a conversion gain control signalreceived via the conversion gain control line.
 7. An image sensorcomprising: a first pixel group sharing a first color filter, the firstpixel group being connected to a first transistor, a first resettransistor, a first floating diffusion region, a first drivingtransistor, and a first selection transistor; and a second pixel groupsharing a second color filter, the second pixel group being disposeddirectly adjacent to the first pixel group in a first direction and isconnected to a second transistor, a second reset transistor, a secondfloating diffusion region, a second driving transistor, and a secondselection transistor, wherein the first transistor and the first resettransistor are connected to the first floating diffusion region and apixel power voltage node, wherein the second transistor and the secondreset transistor are connected to the second floating diffusion regionand the pixel power voltage node, wherein the first color filter isdifferent from the second color filter, and wherein each of the firstpixel group and the second pixel group comprises 2×2 photoelectricconversion elements.
 8. The image sensor of claim 7, further comprising:a third pixel group sharing a third color filter disposed directlyadjacent to the first pixel group in a second direction perpendicular tothe first direction; and a fourth pixel group sharing a fourth colorfilter disposed directly adjacent to the second pixel group in thesecond direction, wherein the first pixel group and the third pixelgroup are connected to a first output line, wherein the second pixelgroup and the fourth pixel group are connected to a second output line,and wherein each of the third pixel group and the fourth pixel groupcomprises 2×2 photoelectric conversion elements.
 9. The image sensor ofclaim 8, wherein the first color filter is a red color filter and thesecond color filter is a green color filter.
 10. The image sensor ofclaim 9, wherein the third color filter is a green color filter and thefourth color filter is a blue color filter.
 11. The image sensor ofclaim 10, further comprising: a third floating diffusion regionconnected to the third pixel group; and a fourth floating diffusionregion connected to the fourth pixel group.
 12. An image sensorcomprising: a first pixel group sharing a first color filter, the firstpixel group being connected to a first transistor, a first resettransistor, a first floating diffusion region, a first drivingtransistor, and a first selection transistor; and a second pixel groupsharing a second color filter, the second pixel group being disposeddirectly adjacent to the first pixel group in a first direction and isconnected to a second transistor, a second reset transistor, a secondfloating diffusion region, a second driving transistor, and a secondselection transistor, wherein the first transistor and the first resettransistor are connected to the first floating diffusion region and apixel power voltage node, wherein the second transistor and the secondreset transistor are connected to the second floating diffusion regionand the pixel power voltage node, wherein the first color filter isdifferent from the second color filter, wherein each of the first pixelgroup and the second pixel group comprises 2×2 photoelectric conversionelements, and wherein the first pixel group and the second pixel groupare connected to a first output line extending in the first direction.13. The image sensor of claim 12, wherein the first color filter is ared color filter and the second color filter is a green color filter.14. The image sensor of claim 12, further comprising: a third pixelgroup sharing a third color filter disposed directly adjacent to thefirst pixel group in a second direction perpendicular to the firstdirection; and a fourth pixel group sharing a fourth color filterdisposed directly adjacent to the second pixel group in the firstdirection, wherein the third pixel group and the fourth pixel group areconnected to a second output line, and wherein each of the third pixelgroup and the fourth pixel group comprises 2×2 photoelectric conversionelements.
 15. The image sensor of claim 14, wherein the third colorfilter is a green color filter and the fourth color filter is a bluecolor filter.
 16. The image sensor of claim 15, further comprising: athird floating diffusion region connected to the third pixel group; anda fourth floating diffusion region connected to the fourth pixel group.